HVAC is an acronym for heating, ventilating, and air conditioning. Refers to the heating, ventilation, air conditioning system installed in a building to regulate temperature. A properly functioning systems cools the air and removes moisture.

Forced ventilation may be used to control humidity or odours. Kitchens and bathrooms typically have mechanical ventilation to control both. Factors in the design of such systems include the flow rate (which is a function of the fan speed and exhaust vent size) and noise level. If the ducting for the fans traverse unheated space (e.g. an attic), the ducting should be insulated as well to prevent condensation on the ducting.
Heat recovery ventilation systems employ heat exchangers to bring the fresh air temperature to room temperature.
Ceiling fans and table/floor fans are very effective in circulating the air in the room. Paradoxically, because heat rises ceiling fans may be used to keep a room warmer.

An air-conditioning system provides heating, cooling, ventilation and humidity control for a building. It is often installed in modern offices and public buildings, but is difficult to retrofit (install in a building that was not designed to receive it) because of the bulky air ducts required. A duct system must be carefully maintained to prevent the growth of pathogenic bacteria in the ducts. The alternative to large ducts to carry the needed air to heat or cool an area is the use of remote coils or split systems. These systems are gaining popularity in commercial buildings although are most often seen in residential application. The remote coil is connected to a remote condenser unit using piping instead of ducts. The units usually have a fan to move air across the coil, although recent innovation have seen static units installed in some large office spaces.

A dehumidifier is an air-conditioning-like device that controls the humiditity of a room or building. They are deployed in basements, which because of their lower temperature have a higher relative humidity. (Conversely a humidifier increases the humidity of a building.)
Air-conditioned buildings often have sealed windows, because open windows would disrupt the attempts of the control system to maintain constant air quality.

This includes air conditioning plants, chillers and ducting systems, which ensure the uniform transfer of the cold or hot air throughout the building.